With the increasing frequency and duration of extreme weather events, the need to provide for losses of electrical power over extended periods has become a necessity for both homes and businesses. In the absence of backup generators, electric power outages result in shutdown of oil and gas-fired heating systems that rely on electrical ignition. During severe weather, when such shutdowns are most likely to occur, the absence of heat for extended periods poses a massive public health threat, particularly to the young, elderly and infirm.
For many families and businesses, installation of a backup gasoline or gas-fired generator is either impractical or unaffordable. Kerosene and propane heaters are bulky and generate unhealthy vapors, as well as posing fire hazards. Portable plug-in electric heaters are clean, relatively safe, and affordable, but they rely on the power grid for their energy. (As used herein, the term “electric heater” designates a heater in which electrical energy is directly converted into heat by one or more resistive heating elements.) While very small battery-powered heaters are available for heating articles of clothing, the large amount of energy demanded for space heating is far beyond the capacity of such systems.
To maintain a 300 square-foot (sq-ft) area at room temperature in temperate winter conditions, for example, requires about 5000 BTU/hr, which equates to nearly 1500 watts (W) of electrical power. Therefore, to heat this 300 sq-ft room for 12 hours demands 18,000 watt-hours (Wh) or 18 kilowatt-hours (kWh) of electrical energy. The amount of energy that a battery can provide before being recharged or replaced is determined by the size/weight of the battery and its energy density. So a rechargeable nickel-cadmium (Ni—Cd) battery weighing one kilogram (kg) and having an energy density of 50 Wh/kg can provide 50 Wh of electrical energy before needing a recharge. This means that a portable heater powered by five such Ni—Cd batteries would have to be recharged every 10 minutes to keep a 300 sq-ft room comfortably warn in winter weather.
In recent years, however, there has been rapid development in battery technology, particularly as applied to electric powered motor vehicles, with the aim of attaining energy densities comparable to those of gasoline (13 kWh/kg). Lithium-ion (Li-Ion) batteries, for example, can have energy densities as high as 250 Wh/kg, so that 5 kg of such batteries could furnish the electrical energy to heat a 300 sq-ft room for nearly an hour before needing to be recharged. Even more advanced metal-air batteries, such as lithium-air and zinc-air batteries, which are currently under development, can attain energy densities in the range of 2000-3000 Wh/kg. As described in the U.S. patent application of Lee et al. (2013/0330639), which is incorporated herein by reference, a lithium air battery designed by Samsung Electronics Co., Ltd., has an energy density of over 3000 Wh/kg, so that 5 kg of such batteries could provide the electrical energy to heat a 300 sq-ft room for 10 hours before needing a recharge.